Since most of my life is now past I feel that I am "too old" to become a Christian. When would it be too late?

There is no age limit, "For he saith, I have heard thee in a time accepted, and in the day of salvation have I succoured thee: behold, now is the accepted time; behold, now is the day of salvation." (II Corinthians 6:2) Today and now are favorite words with God. As long as we are alive on this earth, it is never too late to start doing what is right. God has foreseen your problems. He said in Deuteronomy 4:29-31" But if from thence thou shalt seek the LORD thy God, thou shalt find him, if thou seek him with all thy heart and with all thy soul. When thou art in tribulation, and all these things are come upon thee, even in the latter days, if thou turn to the LORD thy God, and shalt be obedient unto his voice; For the LORD thy God is a merciful God; he will not forsake thee, neither destroy thee, nor forget the covenant of thy fathers which he sware unto them." Regardless of your age, God still loves you and the simple fact that you are reading this shows that you still have an opportunity to accept Jesus as your personal Saviour. Please, don't wait any longer, for this could be the very last time that He speaks to you.